This invention relates to a continously variable friction gear transmission.
One friction gear transmission has been described, for example, in the Applicant""s WO 99/05433. It has input and output discs, which are placed coaxially to a common shaft, are arranged in pairs and have toroid-shaped inner faces, the same as friction gears situated between the pairs of input and output discs. Said friction gears are in frictional contact both with the input discs and the output discs and transmit the torque that is transmitted to them by the input disc to the output disc by means of a frictional engagement contact, the rotational speed of the friction gears being higher the greater the distance is between their contact point with the input disc and the axis of rotation. The rotational speed of the output disc is to the contrary, higher the nearer the contact point between friction gear and output disc lies on the axis of rotation. By swinging the friction gears, accordingly, it is possible to continuously and to arbitrarily adjust the rotational speed of the output disc. To this end, the axes of rotation of the friction gears are supported on a carrier controllable via a swinging device. Both input discs of both transmission units are here non-rotatably connected with a torque shaft while both output discs of both transmission units, which in the transmission are disposed with mirror symmetry to each other, are situated upon a common bushing rotatably supported upon the torque shaft. The torque shaft is traversed by an input shaft which is connected with a starting element of a motor vehicle, such as a torque converter or a wet-running starting clutch of the prime mover of the vehicle.
One other friction gear transmission was disclosed in WO 99/05434. In this friction gear transmission, a power frame is loosely secured to the transmission housing, said power frame has an upper frame bracket, a lower frame bracket, transverse yokes for fastening trunnions and carriers for the friction gears, the same as a cup-shaped bearing element that connects the upper frame bracket with the lower frame bracket. Said bearing element is situated between the two hollow spaces where both transmission units are located and is axially traversed by the torque shaft. The frame brackets can be screwed or welded with the power frame which power frame carries the essential elements of the variator and is utilizable as a pre-assembled unit in the transmission housing.
After fitting the variator parts outside the transmission housing and inserting the pre-assembled variator in the transmission housing, other parts such as a starting element, a reversing set and a hydraulic control are to be installed in the transmission housing. Only after assembly of all parts is it possible to test the operating capacity of the variator. In case of defective behavior of the variator, prior to actual service diagnosis, the disassembly of the additional parts like the starting element, etc., is required before the pre-assembled variator can be removed. But such assembly and disassembly works are associated with great expenditure of time and costs.
The problem on which this invention is based is to develop a variator not only as pre-assembled construction unit but as on autarchic construction unit capable of operation prior to installation in the transmission housing.
According to the invention, it is provided that the supporting pistons for the trunnions are integrated in the power frame so that, prior to installation in the transmission housing, the variator is developed as an operationally capable autarchic unit which can be fully tested before installation and only after successful inspection is fitted in the transmission housing as a construction part.
The power frame makes a pre-assembly outside the transmission housing possible so that the supporting pistons for the trunnions can be easily integrated in them. At the same time, the feedback rod for the control valve, designed as a square slide, can constitute the interface; also possible is an integration in the power frame of said square slide, including or excluding the stepping motor.
In an advantageous embodiment, the discs of the transmission units can be lubricated or cooled via the upper and/or lower posts, the power frame absorbing the lubricant pressure, through one or more ducts situated in it, and relaying it via associated ducts to the critical parts of the discs.
In another preferred embodiment, a suppressing labyrinth for ventilation of the transmission housing is provided in the power frame, since a retention of the highly volatile friction fluid there by is ensured.
One other advantage is to be seen in that the integration of the complete output constants, including the gear wheel of the side shaft and the full support of both gear wheels in the power frame, make a simple assembly and an advantageous tolerance draft possible for both friction gears, such as needed for the extremely quickly rotating friction gears.